linux-kernel - Re: [PATCH 3/6] pwm: sun4i: Add a quirk for bus clock

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Message-ID: <20190729161435.5bnj3ikocsyep4dd@pengutronix.de>
Date:   Mon, 29 Jul 2019 18:14:35 +0200
From:   Uwe Kleine-König 
        <u.kleine-koenig@...gutronix.de>
To:     Jernej Škrabec <jernej.skrabec@...l.net>
Cc:     mark.rutland@....com, linux-pwm@...r.kernel.org,
        devicetree@...r.kernel.org, linux-sunxi@...glegroups.com,
        linux-kernel@...r.kernel.org, mripard@...nel.org, wens@...e.org,
        robh+dt@...nel.org, thierry.reding@...il.com,
        kernel@...gutronix.de, linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH 3/6] pwm: sun4i: Add a quirk for bus clock

Hello Jernej,

On Mon, Jul 29, 2019 at 05:48:36PM +0200, Jernej Škrabec wrote:
> Dne ponedeljek, 29. julij 2019 ob 08:38:25 CEST je Uwe Kleine-König 
> napisal(a):
> > Hello,
> > 
> > On Fri, Jul 26, 2019 at 08:40:42PM +0200, Jernej Skrabec wrote:
> > > H6 PWM core needs bus clock to be enabled in order to work.
> > > 
> > > Add a quirk for it.
> > > 
> > > Signed-off-by: Jernej Skrabec <jernej.skrabec@...l.net>
> > > ---
> > > 
> > >  drivers/pwm/pwm-sun4i.c | 15 +++++++++++++++
> > >  1 file changed, 15 insertions(+)
> > > 
> > > diff --git a/drivers/pwm/pwm-sun4i.c b/drivers/pwm/pwm-sun4i.c
> > > index 1b7be8fbde86..7d3ac3f2dc3f 100644
> > > --- a/drivers/pwm/pwm-sun4i.c
> > > +++ b/drivers/pwm/pwm-sun4i.c
> > > @@ -72,6 +72,7 @@ static const u32 prescaler_table[] = {
> > > 
> > >  };
> > >  
> > >  struct sun4i_pwm_data {
> > > 
> > > +	bool has_bus_clock;
> > > 
> > >  	bool has_prescaler_bypass;
> > >  	bool has_reset;
> > >  	unsigned int npwm;
> > > 
> > > @@ -79,6 +80,7 @@ struct sun4i_pwm_data {
> > > 
> > >  struct sun4i_pwm_chip {
> > >  
> > >  	struct pwm_chip chip;
> > > 
> > > +	struct clk *bus_clk;
> > > 
> > >  	struct clk *clk;
> > >  	struct reset_control *rst;
> > >  	void __iomem *base;
> > > 
> > > @@ -382,6 +384,16 @@ static int sun4i_pwm_probe(struct platform_device
> > > *pdev)> 
> > >  		reset_control_deassert(pwm->rst);
> > >  	
> > >  	}
> > > 
> > > +	if (pwm->data->has_bus_clock) {
> > > +		pwm->bus_clk = devm_clk_get(&pdev->dev, "bus");
> > 
> > Similar to my suggestion in patch 2: I'd use devm_clk_get_optional() and
> > drop struct sun4i_pwm_data::has_bus_clock.
> 
> This one is not so simple. This patch has incorrect logic. Correct logic would 
> be to use "devm_clk_get(&pdev->dev, NULL)" for variants without bus clock as 
> it is done already and "devm_clk_get(&pdev->dev, "bus")" and 
> "devm_clk_get(&pdev->dev, "mod")" for variants with bus clock.

Then maybe something like the following?:

	busclk = devm_clk_get_optional(..., "bus");
	modclk = devm_clk_get_optional(..., "mod");

	/*
	 * old dtbs might have a single clock but no clock names. Fall
	 * back to this for compatibility reasons.
	 */
	if (!modclk) {
		modclk = devm_clk_get(..., NULL);
	}
 
> You see, DT nodes for other variants don't have clock-names property at all. 
> If it would be specified, it would be "mod". So, DT nodes for other variants 
> have "mod" clock specified on first place (the only one), while H6 DT node will 
> have "mod" clock specified on second place (see one of e-mails from Maxime), so 
> "NULL" can't be used instead of "mod" in both cases.
> 
> So I would say quirk is beneficial to know if you have to look up clocks by 
> name or you just take first clock specified.

Best regards
Uwe

-- 
Pengutronix e.K.                           | Uwe Kleine-König            |
Industrial Linux Solutions                 | http://www.pengutronix.de/  |